washington — – Bit by bit, the walls are closing in on Hillary Rodham Clinton. By just about every measure, including total votes, total delegates, and money raised, she is trailing Barack Obama in their pitched battle for the Democratic presidential nomination. And in the most important category where she's still ahead – superdelegates – her lead is shrinking.

Thus far this week, three superdelegates – party leaders and elected officials who can support whomever they want at the August convention – have broken for Senator Obama while Senator Clinton hasn't won any. It is highly unlikely that Clinton can overtake Obama in the "pledged delegate" count – those won in primaries and caucuses – but it is also impossible for Obama to secure the nomination just on pledged delegates. Thus, the superdelegates will decide the nomination.

Thursday's stunning announcement that Obama had raised more than $40 million in March, with 218,000 new donors that month, dealt another blow to Clinton. Her campaign has not released its own March figure yet, but said it will come in below Obama's.

So, can Clinton actually still win the nomination? In theory, yes, analysts say. But she would have to win just about every remaining contest, and then persuade enough superdelegates that she has a better chance than Obama of beating the presumptive Republican nominee, Sen. John McCain of Arizona, in November.

The easiest way for that to happen would be for a bombshell revelation or major gaffe by Obama that would cause delegates, and voters – as reflected in national polls – to abandon the Illinois senator. Short of that scenario, Clinton and her team are fast running out of options.

"Convincingly" means by double-digits, he says. Then Clinton would have to pull off an upset in North Carolina (May 6) or Oregon (May 20), where Obama is favored. "Most people looking at the last 10 events or so see a bit of an edge for Clinton, but with Obama having significant places to look for wins as well," Mr. Jillson adds.

For now, though, the trends seem to be heading in Obama's direction – even in Pennsylvania, where polls showed Clinton with a lead in the mid-to-high teens until recently. The latest Quinnipiac Poll shows Clinton with a nine-point lead in Pennsylvania, a figure that makes sense to political analysts in the state.

Pennsylvania's demographics – large populations of working-class, older, and Roman Catholic voters – play to Clinton's advantage. But a wave of new registrations in the state could spell trouble for her, as the Obama campaign has worked hard to identify new voters. "[Pennsylvania] is absolutely critical for her," says Terry Madonna, head of the Franklin and Marshall College Poll. "I think she wins here, but for the first time, I'm thinking he could upset her. It's a long-shot, but I see a way."

Several weeks ago, Mr. Madonna laid out a path to victory for Obama in Pennsylvania in a column on Realclearpolitics.com. The path is, ironically, one that Gov. Ed Rendell – a Clinton supporter – carved out in 2002 in his gubernatorial nomination battle with now-Sen. Bob Casey, who recently came out for Obama.

Governor Rendell succeeded by concentrating his efforts (and winning big) in his base areas (Philadelphia and its suburbs); winning big in swing areas; and managing turnout statewide, in part by registering new voters.

Still, Clinton remains a strong favorite in Pennsylvania – and thus, her campaign is likely to survive at least into May. Ken Smukler, a Democratic consultant in Philadelphia, warns against reading too much into the fluctuations in polls. "My sense is this electorate is very volatile right now," he says. And, he adds, "the newly registered voters are not being sampled in any poll right now. One could argue they're Obama voters."

But he also won't count Clinton out. And he believes, despite Obama's money edge, Clinton will have enough to match him on TV in Pennsylvania.

The Clinton team is adamant that the superdelegates will, after all the votes are cast, "do the right thing" for the party and for the country. In a conference call Thursday, campaign spokesmen once again argued that Clinton is more electable, citing polls that show her beating Senator McCain in key states, such as Florida and Ohio, while Obama loses.

"Senator Obama's lead is almost entirely from caucuses," says Mark Penn, a senior Clinton strategist. "Will he have a lead at all coming out of the high turnout primaries? That's certainly up for grabs, and we'll see what comes out after this next run of states, as well as who's in a better position then to take on and beat Senator McCain."

According to the Associated Press, Obama leads in the overall delegate count 1,634 to 1,500, with 2,024 needed to secure the nomination. Clinton leads in superdelegates, 250 to 220 out of a total 794. In the popular vote, Obama leads by about 700,000, but that does not include the votes in Michigan and Florida, which were held outside party rules. But even counting Clinton's votes in both states, she still does not catch up to Obama.